1. Field of the Invention
The present invention relates to a magnetic random access memory (MRAM) comprising a magneto-resistance element and a method of writing data in the magnetic random access memory.
2. Description of the Related Art
In recent years, a magnetic random access memory (MRAM) utilizing the tunnel magneto-resistance (MRAM) effect has been proposed as a semiconductor memory.
In a memory cell of the MRAM, an MTJ (Magnetic Tunneling Junction) element is provided at each point of intersection between a bit line and a word line as an information storage element. If a data write is carried out, currents are allowed to flow through a selected bit line and a selected word line, respectively, to generate a composite magnetic field. Then, the composite magnetic field is used to write data in an MTJ element in the selected cell located at the point of intersection between the selected bit line and the selected word line. On the other hand, to read data from a memory cell, a read current is allowed to flow through the MTJ element in the selected cell. Then, “1” or “0” data is read on the basis of the change in the resistance of the magnetized state of the MTJ element.
In such an MRAM, when a data write is carried out, the write current magnetic field may affect semi-selected cells selected by one of the selected bit line and the selected bit line. Then, data may be erroneously written in the semi-selected cells. This is called a disturbance. The avoidance of disturbance is considered to be one of the most important objects in the development of MRAMs. However, an asteroid characteristic is sensitive to the shape of the MTJ element or the like. Accordingly, the fine-grained structure of the element may further significantly affect the asteroid characteristic. Thus, the number of miswrites in semi-selected cells increases with decreasing size of the element. Then, the disturbance becomes more serious. To avoid this problem, the write current must be increased in order to prevent miswrites in semi-selected cells. There are MRAMs based on a toggle system using a weakly coupled stacked recording layer. However, this system must also increase the write current.